Display apparatus with replaceable electroluminescent element

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of the earlier filed provisional U.S. Patent Application Ser. No. 60/697,297 filed Jul. 8, 2005.

FIELD OF THE INVENTION

The present invention relates generally to electroluminescent devices and more particularly to an electroluminescent housing with a replaceable electroluminescent sheet adapted for luminescent displays.

BACKGROUND OF THE INVENTION

Prior art electroluminescent apparatus such as signs, segmented displays, dot-matrix displays, moving messages, computer and TV monitors may be comprised of an electroluminescent (EL) device which includes two electrodes and an electroluminescent material or phosphor layer sandwiched between. Typically, the electrodes are permanently attached to the phosphor layer. Over time, the phosphor loses brightness due to aging; however, the electrodes are still functional. It would therefore be beneficial to provide an electroluminescent apparatus which extends the useful life of an electroluminescent device by allowing for replacement of the electroluminescent phosphor layer.

Typical electroluminescent devices also consist of a single disposable unit, which may require that device be discarded once the phosphors have lost some of their brightness. Although the phosphor layer may be one of the least expensive components of the apparatus, the entire device is discarded. It would therefore be beneficial to provide a housing which allows for replacement of the phosphor layer, while allowing the remaining components to be reused.

Electroluminescent phosphor brightness decays based upon the applied voltage, frequency and waveform provided by the electronic circuitry. At a constant initial voltage and frequency, brightness will exponentially decrease with time of operation. Typically, the electroluminescent phosphor is preliminarily aged using a technique referred to as “rapid aging” by aging the devices after fabrication. However, this rapid aging leads to a reduction in brightness and useful lifetime. It would therefore be beneficial to provide a control circuitry which automatically controls the brightness.

It would also be beneficial to have an electroluminescent apparatus which provides an increase in brightness of the electroluminescent sheets and which is reusable, and allows the replacement of the electroluminescent sheet without the necessity to discard the entire device at the end of its useful lifetime.

SUMMARY OF THE INVENTION

In the embodiments of the present invention the aforementioned problems are addressed by providing an electroluminescent apparatus that utilizes a replaceable electroluminescent sheet which, in operation of the apparatus, is held between two electrodes that are within a resealable housing which may be opened and closed so that a used electroluminescent sheet may be removed from between the electrodes and replaced at the end of its usable lifetime. The housing has front and rear panels associated with the respective electrodes, at least one of the panels being transparent. The electroluminescent sheet is held between the electrodes when the housing is closed and may be removed from between the electrodes and replaced when the housing is opened. A compression structure is provided in the housing to assure close physical contact between the electrodes and the electroluminescent sheet when the apparatus is in operation. Other aspects of the invention include an inflatable compressing structure, an alignment structure within the housing for alignment of the electroluminescent sheet, transparent electrodes and various drivers that may be used allowing for monochrome or color displays. A housing having an envelope configuration, a roll of electroluminescent sheets or a tiled structure allowing for larger electroluminescent displays is also within the scope of the present invention. A method of replacing an electroluminescent device, which is part of the present invention, includes providing a resealable housing with first and second panels, positioning a sheet between the panels, operably sandwiching the sheet between a first and second electrode associated with respective panels and resealably securing the housing with the sheet positioned therein.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idrefs="DRAWINGS">FIG. 1</figref> is a perspective view of an embodiment of an electroluminescent system in accordance with the present invention, shown in an open condition.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a cross-sectional view of the system according to the present invention, shown in an operative condition.

<figref idrefs="DRAWINGS">FIG. 3</figref> is a cross-sectional view of alternative aspect of the electroluminescent system having an inflatable membrane in accordance with to the present invention.

<figref idrefs="DRAWINGS">FIG. 3</figref><i>a </i>is a cross-sectional, diagrammatic view of a second alternative aspect of the electroluminescent system having an inflatable compression structure in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 4</figref><i>a </i>is a cross-sectional, diagrammatic view of an aspect of an electroluminescent device associated with a front panel in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 4</figref><i>b </i>is a cross-sectional view of an alternative aspect of an electroluminescent sheet in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 4</figref><i>c </i>is a cross-sectional view of an alternative aspect of the electroluminescent sheet in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a cross-sectional view of an alternative aspect of a compression structure in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 6</figref> is a perspective view of an aligning structure in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 7</figref> is a side perspective view of an alignment reinforcing structure in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 8</figref> is a cross-sectional view of an alternative housing in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 8</figref><i>a </i>is a cross-sectional view of an alternative aspect of the housing of <figref idrefs="DRAWINGS">FIG. 8</figref> in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 8</figref><i>b </i>is a cross-sectional view of another alternative aspect of the housing of <figref idrefs="DRAWINGS">FIG. 8</figref> in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 9</figref> is a partial cross-sectional view of a second alternative housing in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 10</figref> is a plan view of an alternative aspect of an electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 11</figref> is a plan view of a second alternative aspect of an electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 12</figref> is a plan view of a third alternative aspect of an electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 13</figref> is a diagrammatic illustration of the electrical field between the electrodes.

<figref idrefs="DRAWINGS">FIG. 14</figref> is a cross-sectional view of an alternative aspect of a transparent electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 15</figref> is a cross-sectional view of another alternative aspect of the transparent electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 16</figref> is a cross-sectional view of a third alternative aspect of the transparent electrode in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 17</figref> is a cross-sectional view of an alternative aspect of an electroluminescent sheet in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 18</figref> is an exploded perspective view of a dot matrix configuration in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 19</figref> is a diagrammatic exploded view of a color dot matrix configuration in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 20</figref> is a diagrammatic, exploded view of an alternative electroluminescent device according to the present invention, including color filters.

<figref idrefs="DRAWINGS">FIG. 21</figref> is a diagrammatic view of a CRT driver in accordance with the present invention.

<figref idrefs="DRAWINGS">FIG. 22</figref> is a perspective view of an alternative aspect of the electroluminescent sheet including a tiled surface.

<figref idrefs="DRAWINGS">FIG. 23</figref> is a cross-sectional view of the tiled electroluminescent sheet of <figref idrefs="DRAWINGS">FIG. 22</figref>.

<figref idrefs="DRAWINGS">FIG. 24</figref> is a cross-sectional view of an alternative aspect of the housing with pixeled rear electrode.

<figref idrefs="DRAWINGS">FIG. 25</figref> is a cross-sectional diagrammatic view of a second alternative aspect of the tiled electroluminescent sheet.

<figref idrefs="DRAWINGS">FIG. 26</figref> is a graph of the brightness characteristic of the electroluminescent sheet.

<figref idrefs="DRAWINGS">FIG. 27</figref> is a partial, perspective view showing grooves in the electrodes for air evacuation.

<figref idrefs="DRAWINGS">FIG. 28</figref> is a perspective view of the separating sheet with openings.

<figref idrefs="DRAWINGS">FIG. 29</figref> is a perspective view of a rear pixeled electrode.

<figref idrefs="DRAWINGS">FIG. 30</figref> is a perspective view of the electroluminescent sheet with photodiodes in accordance with the present invention.

DETAILED DESCRIPTION

I. Introduction.

As required, embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention as desired.

II. Electroluminescent Apparatus.

Housing

Referring to <figref idrefs="DRAWINGS">FIGS. 1-2</figref>, in an embodiment of the present invention an electroluminescent (EL) apparatus generally indicated by reference numeral <b>30</b> includes first and second spaced electrodes <b>40</b>, <b>42</b>, and a housing <b>50</b> adapted to receive a replaceable electroluminescent sheet <b>60</b> sandwiched between first and second electrodes <b>40</b>, <b>42</b> to present an electroluminescent device <b>70</b>. The housing <b>50</b> generally includes front and rear panels <b>52</b>, <b>54</b> spaced from each other, the front panel <b>52</b> being associated with the first transparent electrode <b>40</b> and the rear panel <b>54</b> being associated with the second electrode <b>42</b>. In operation, the housing <b>50</b> may be opened and closed. When closed, the front and rear panels <b>52</b>, <b>54</b> in association with first and second electrodes <b>40</b>, <b>42</b> receive the electroluminescent sheet <b>60</b> therebetween. When the housing <b>50</b> is open, the electroluminescent sheet <b>60</b> may be removed and replaced with another electroluminescent sheet.

The housing <b>50</b> is illustrated in the open position in <figref idrefs="DRAWINGS">FIG. 1</figref> with the front panel <b>52</b> mechanically secured to the rear panel <b>54</b> with, for example but not as a limitation, a hinge <b>58</b> or other mechanical structure operably connected between the panels <b>52</b>, <b>54</b> for replacement of the electroluminescent sheet <b>60</b>. As shown, a complementary pair of hinges <b>59</b> connects the panels <b>52</b>, <b>54</b> and the housing <b>50</b> along with an optional mounting bracket <b>86</b> for mounting the apparatus <b>30</b>. In addition, the housing <b>50</b> may include an optional locking mechanism <b>88</b> with a release handle <b>90</b> for securing the housing <b>50</b> in a closed condition. Housing <b>50</b> may include an optional locking mechanism <b>91</b> for securing the housing <b>50</b> to the bracket <b>86</b> after replacement of the EL sheet <b>60</b>.

Opening the housing <b>50</b> using the hinges <b>58</b>, the electroluminescent sheet <b>60</b> can be readily replaced. After closing the hinged rear panel or back door <b>54</b>, the electroluminescent sheet <b>60</b> may be pressed against the first electrode <b>40</b> (which should be transparent) by a compressing structure <b>80</b> discussed hereinbelow. Housing <b>50</b> may contain an overlay (not shown) between front panel <b>52</b> and front electrode <b>40</b>. The overlay may present visual indicia or be any semi or partially transparent material, optionally presenting an image.

<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates the housing <b>50</b> in a closed position with the front and rear panels <b>52</b>, <b>54</b> in association with first and second electrodes <b>40</b>, <b>42</b> sandwiching the electroluminescent sheet <b>60</b>. The compressing structure <b>80</b> is illustrated in <figref idrefs="DRAWINGS">FIG. 2</figref> configured to compress the first electrode <b>40</b> in relation to the second electrode <b>42</b>. In <figref idrefs="DRAWINGS">FIG. 2</figref>, any gap between the electrodes <b>40</b>, <b>42</b> and the electroluminescent sheet <b>60</b> are for illustrative purposes only. While the housing <b>50</b> is in the closed position, there will be no noticeable gap between the electrodes <b>40</b>, <b>42</b> and the electroluminescent sheet <b>60</b>. The housing <b>50</b> is optionally illustrated with the front panel <b>52</b> being at least partially transparent, or having an opening associated with a transparent material (for example, a glass panel <b>56</b>) positioned behind the front panel <b>52</b>. The compressing structure <b>80</b> is generally fabricated from flexible, compressible material such as, but not limited to, rubber or sponge or some other resilient material. Generally, the compressing structure <b>80</b> is positioned between the second electrode <b>42</b> and the rear panel <b>54</b>.

<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates an alternative rear panel <b>54</b><i>a </i>having a convex surface and a compressing structure <b>80</b><i>b </i>constructed of a flexible, compressible material <b>82</b> having a convex surface and adapted to provide uniform pressure against the second electrode <b>42</b>. In this way the electrodes <b>40</b>, <b>42</b> may be optimally compressed to the electroluminescent sheet <b>60</b>.

Inflatable Compressing Structure

<figref idrefs="DRAWINGS">FIG. 3</figref><i>a </i>illustrates an alternative configuration of the apparatus <b>30</b> having an inflatable compressing structure, also referred to herein as an inflatable structure <b>80</b><i>c</i>, positioned between the rear panel <b>54</b> and the EL device <b>70</b> which includes the sheet <b>60</b> sandwiched between the first and second electrodes <b>40</b>, <b>42</b>. In this configuration the inflatable structure <b>80</b><i>c </i>has an intake <b>94</b> in fluid communication with a source of pressure, for example, an air or hydraulic pump (not shown) for inflating the structure <b>80</b><i>c</i>. As the structure <b>80</b><i>c </i>inflates, the EL device <b>70</b> is pressed together. An air gap in the EL device <b>70</b> may be reduced by using at least two flexible components in the EL device <b>70</b> (such as the electroluminescent sheet <b>60</b> or the first or second electrode <b>40</b>, <b>42</b>). As structure <b>80</b><i>c </i>inflates the flexible components press against each other and the front panel <b>52</b>, thereby providing a closer physical connection in the EL device <b>70</b>.

<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates a second alternative inflatable compressing structure <b>180</b> including a flexible membrane <b>190</b> incorporated within a rear panel <b>154</b> to define a chamber <b>192</b> therebetween. The rear panel <b>154</b> also has an intake <b>194</b> that is in communication with the pressure source (not shown) for inflating the membrane <b>190</b> and assuring a closer physical connection between the electroluminescent sheet <b>60</b> and the corresponding electrode <b>142</b>.

Electroluminescent Sheet

The electroluminescent sheet or element <b>60</b> illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref><i>a </i>is shown between the first and second electrodes <b>40</b>, <b>42</b>, overlying the front panel <b>52</b>. The thickness of the sheet <b>60</b> may vary depending on the sheet's physical dimensions. Up to approximately 8.5×11 inches in size, the electroluminescent sheet <b>60</b> can be in the range of 25-50 microns thick. For larger sizes, handling of the electroluminescent sheet <b>60</b> may become more difficult, and the thickness may need to be increased. In addition, a proportional increase of the voltage between the electrodes <b>40</b>, <b>42</b> may be required to maintain the same brightness of the electroluminescent sheet <b>60</b>.

In general, the electroluminescent sheet <b>60</b> is a flexible film in the range of 25-100 microns thick and can be fabricated in sheets or rolls. A sheet of plastic or organic resin film <b>92</b> can be used with impregnated EL phosphorous powder <b>62</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref><i>a</i>. The sheet <b>60</b> can also include areas of different colors, areas without phosphors <b>62</b> or areas selectively coated with another material such as, but not limited to, conventional ink. Selectively coating the sheet may provide a visual illustration or indicia. In addition, reducing the amount of phosphorous powder <b>62</b> associated with the electroluminescent sheet <b>60</b> may provide an economic benefit.

The replaceable electroluminescent sheet <b>60</b> is illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref><i>a </i>having impregnated electroluminescent phosphor <b>62</b>. Alternatively, the electroluminescent phosphor <b>62</b> may be deposited on one side of an insulative film <b>63</b> as shown in <figref idrefs="DRAWINGS">FIG. 4</figref><i>b </i>or plural insulative films <b>63</b> may be provided as shown in <figref idrefs="DRAWINGS">FIG. 4</figref><i>c</i>, sandwiching the electroluminescent phosphor <b>62</b> therebetween.

Operation

In operation the present invention may be practiced by providing the housing <b>50</b> having front and rear panels <b>52</b>, <b>54</b>, associating first and second electrodes <b>40</b>, <b>42</b> respectively with the panels <b>52</b>, <b>54</b>, positioning the replaceable electroluminescent sheet <b>60</b> within the housing <b>50</b> between the panels <b>52</b>, <b>54</b> and operably sandwiching the sheet <b>60</b> between the electrodes <b>40</b>, <b>42</b>, and then releasably securing the housing <b>50</b> with the sheet <b>60</b> positioned therebetween.

Alignment Structure

Electroluminescent sheets <b>60</b> may be adapted for color display through the use of tricolor phosphors which may require precise positioning of the electroluminescent sheet <b>60</b>. Tolerance may be limited based on the configuration of the electrodes <b>40</b>, <b>42</b>. Therefore, the positioning of the electroluminescent sheet <b>60</b> should be generally fixed before closing the housing <b>50</b>.

Fixing the position of the electroluminescent sheet <b>60</b> may be accomplished using a variety of techniques including adhesives or mounting structure like pegs and peg receivers. <figref idrefs="DRAWINGS">FIG. 6</figref> illustrates the use of the electroluminescent sheet <b>60</b> having two or more alignment receivers or peg holes <b>66</b> with matching alignment pegs <b>64</b> operably positioned within the housing <b>50</b> (not shown). Although <figref idrefs="DRAWINGS">FIG. 6</figref> illustrates the receivers <b>66</b> as being round for receiving the round pegs <b>64</b>, the receivers <b>66</b> can have varying shapes and sizes such as but not limited to round, square or of any other shape that fixes the position of the sheet <b>60</b>. Pegs <b>64</b> can also have varying, complementary, shapes and sizes and may be arranged in a horizontal-mounting arrangement within the housing <b>50</b>, or they may be mounted at an upward angle, or with upwardly extending hooks.

In general, the alignment pegs <b>64</b> may be associated with either the front or rear panel <b>52</b>, <b>54</b> of the housing <b>50</b> and the sheet <b>60</b> can have plural alignment receivers <b>66</b> placed thereon for receiving the pegs <b>64</b> and aligning the sheet <b>60</b> with first and second electrodes <b>40</b>, <b>42</b> (not shown). Optionally, a reinforcement layer <b>68</b><i>b </i>having plural reinforcement receivers <b>66</b><i>b </i>may be associated with the sheet <b>60</b> and configured to receive the alignment pegs <b>64</b>, reinforcing and at least partially overlying the alignment receivers <b>66</b>, as shown in <figref idrefs="DRAWINGS">FIG. 7</figref>.

Envelope Housing

An alternative configuration of a housing <b>250</b> in an open condition is illustrated in <figref idrefs="DRAWINGS">FIG. 8</figref> having a front panel <b>252</b>, a rear panel <b>254</b> and a resealable gasket <b>292</b> located between them having complementary sealing structure for releasably sealing the housing <b>250</b>. The front and rear panels <b>252</b>, <b>254</b> are associated with a first and second electrodes <b>240</b>, <b>242</b> respectively. In this configuration, the housing <b>250</b> encases the electroluminescent sheet <b>260</b>. The front and rear panels <b>252</b>, <b>254</b> sealed by the gasket <b>292</b> define a chamber <b>298</b>. The housing <b>250</b> may also include a structure <b>296</b> in fluid communication with the housing <b>250</b> for depressurizing the housing <b>250</b>. As the housing is depressurized, the sheet <b>260</b> and electrodes <b>252</b>, <b>254</b> shift, promoting closer physical contact therebetween. For example, a vacuum pump (not shown) may be used to depressurize the housing <b>250</b> with one of the panels <b>252</b>, <b>254</b> being flexible.

After the housing <b>250</b> is closed and the gasket <b>292</b> is sealed, the air from the housing <b>250</b> may be evacuated, pressing electrodes <b>240</b>, <b>242</b> towards the sheet <b>260</b>. Air may be evacuated with a vacuum pump or with another type of device with or without a vacuum tank.

The configuration of the housing <b>250</b> may be described as a sealed envelope, optionally having at least one transparent panel and at least one flexible panel. After the electroluminescent sheet <b>260</b> is installed, the envelope <b>250</b> may be sealed by a releasable complementary seal, zipper, mechanical clip or closure which provides a hermetic seal.

Alternatively, as illustrated in <figref idrefs="DRAWINGS">FIGS. 8</figref><i>a </i>and <b>8</b><i>b</i>, the housing <b>250</b><i>b</i>, <b>250</b><i>c </i>may include an adhesive tape joint <b>288</b> replacing the gasket <b>292</b>, sealing the front and rear panels <b>252</b>, <b>254</b> of the alternative housing <b>250</b><i>b</i>, <b>250</b><i>c</i>, around first and second electrodes <b>240</b>, <b>242</b> with electroluminescent sheet <b>260</b> sandwiched therebetween.

Rolled Electroluminescent Sheet

For an electroluminescent phosphor, its lifetime is inversely proportional to its brightness. When high brightness is required and frequent replacement of electroluminescent sheets may be desired, an alternative embodiment of the electroluminescent housing <b>350</b>, illustrated in <figref idrefs="DRAWINGS">FIG. 9</figref>, may be used. A supply or roll <b>360</b> of sequential electroluminescent sheets <b>362</b> is received within the housing <b>350</b>. The roll <b>360</b> may be fabricated using flexible materials including, but not limited to, plastic or organic resin film, providing flexible electroluminescent sheets <b>362</b> having a small bend radius. The sheets <b>362</b> may be layered to sandwich the electroluminescent phosphor particles of sequential sheets <b>362</b>. The supply <b>360</b> may be fabricated from individual sheets <b>362</b> sequentially attached together or the supply <b>360</b> may be fabricated as one long sheet with individual sequential sheets or areas <b>362</b> located therein. The housing <b>350</b> receives the supply <b>360</b> of flexible material which presents plural spaced apart sequential electroluminescent sheets <b>362</b> positioned within the housing <b>350</b>.

The housing <b>350</b> is illustrated in the open position having front and rear panels <b>352</b>, <b>354</b> defining a display area <b>356</b>. The display area <b>356</b> includes a first and second electrode <b>340</b>, <b>342</b> contained within the housing <b>350</b> and associated with the front and rear panels <b>352</b>, <b>354</b> respectively. The housing <b>350</b> also contains a take-up structure <b>364</b> which receives the sequential electroluminescent sheets <b>362</b>. As the sheet <b>362</b> is spent or depleted of its luminescent properties, the spent electroluminescent sheet <b>362</b> is sequentially moved from the supply <b>360</b> through the display area <b>356</b> between the first and second electrodes <b>340</b>, <b>342</b> to the take-up structure <b>364</b> positioning the next sequential sheet <b>362</b> within the display area <b>356</b>. After each sequential electroluminescent sheet <b>362</b> traverses the display area <b>356</b> a compression mechanism <b>380</b> moves the rear panel <b>354</b> forward and compresses the EL device <b>370</b>, thereby promoting closer physical contact between the sheet <b>362</b> and the electrodes <b>340</b>, <b>342</b>.

The configuration of the supply of sequential sheets <b>360</b> within the housing <b>350</b> is similar to film cameras or projectors. The electrodes <b>340</b>, <b>342</b> may optionally be frictionally pressed against the sequential sheet <b>362</b> by mechanical means, compressed air, vacuum, or any other known method. When the brightness of the portion of the electroluminescent sheet <b>360</b> positioned within the display area <b>356</b> falls below a desired level, the next sequential sheet <b>362</b> within the electroluminescent roll <b>360</b> is positioned within display area <b>356</b>. This can be configured in either a vertical or horizontal orientation. Sequential movement of the sheets <b>362</b> may be similar to advancing a roll of film in a camera. All operations can be done manually or automatically with a drive mechanism <b>382</b> or a release structure.

For example, a compression mechanism <b>380</b> may be synchronized with the drive mechanism <b>382</b> such that the compression mechanism <b>380</b> is uncompressed when the drive mechanism <b>382</b> operates. After the drive mechanism <b>382</b> positions the next sequential electroluminescent sheet <b>362</b> in the display area <b>356</b>, the compression mechanism <b>380</b> promotes closer physical contact between the electrodes <b>340</b>, <b>342</b> and the sheet <b>362</b>.

Transparent Electrodes

Instead of indium tin oxide (ITO) films, plural thin parallel electrical contacts or wires <b>564</b> may be used as transparent electrodes as shown in <figref idrefs="DRAWINGS">FIGS. 10-13</figref>. The wires <b>564</b> can be connected together forming a single integrated and larger transparent electrode, as shown in <figref idrefs="DRAWINGS">FIG. 10</figref> or used separately (<figref idrefs="DRAWINGS">FIG. 11</figref>) as pixel electrodes for displays and controlled by a display driver <b>544</b>. For larger displays, wires <b>564</b> can be connected together in parallel at <b>564</b><i>a </i>to form individual electrodes <b>540</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 12</figref>. The gap between first and second electrodes <b>540</b>, <b>542</b> can be relatively small allowing a strong electrical field in the electroluminescent sheet <b>560</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 13</figref>. Large gaps are not desirable because as distance between the electrodes <b>540</b>, <b>542</b> increases, the required voltage must also increase to provide the same electrical field and same brightness of the electroluminescent sheet <b>60</b>.

<figref idrefs="DRAWINGS">FIGS. 14-16</figref> illustrate an alternative embodiment with a transparent electrode <b>540</b> consisting of parallel electrical contacts <b>564</b> generally fabricated from a metal. Electrical contacts <b>564</b> may be incorporated within a transparent material <b>568</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 14</figref>. Alternatively, parallel wires <b>564</b> may be associated with a proximal or distal side <b>568</b><i>a</i>, <b>568</b><i>b </i>of the transparent material <b>568</b> (<figref idrefs="DRAWINGS">FIG. 15-16</figref>), or sandwiched between two transparent materials such as, but not limited to, glass or plastic. Optionally, a coating may be applied to the electrical contacts <b>564</b>, presenting a smooth electrode surface.

An increase of the distance between the wires <b>564</b> and the second electrode <b>542</b> provides a wider and more uniform luminescence of the electroluminescent sheet <b>560</b>, but this configuration also requires the voltage to be increased to maintain the same sheet brightness. This is illustrated in <figref idrefs="DRAWINGS">FIG. 13</figref>, with a plurality of lines of electrical force <b>574</b> extending between the first electrode <b>540</b> to the second electrode <b>542</b> through the sheet <b>560</b>. As the electrodes are separated from each other, these lines of electrical force <b>574</b> become more uniform within the sheet <b>560</b>.

Another embodiment of the invention is illustrated in <figref idrefs="DRAWINGS">FIG. 17</figref> with a phosphor layer <b>560</b><i>b </i>being associated with the optionally transparent second electrode <b>542</b>, in an alternative embodiment of an electroluminescent sheet <b>570</b> received within a housing such as shown at <b>50</b> in <figref idrefs="DRAWINGS">FIG. 2</figref>. As previously set forth, the alternative housing (not shown) has a front and rear panel <b>52</b>, <b>54</b> and first electrode <b>40</b> associated with one of said panels. The second electrode <b>542</b> has a continuous surface as shown in <figref idrefs="DRAWINGS">FIG. 17</figref> and is combined with the electroluminescent sheet <b>570</b>. The second electrode <b>542</b> may be fabricated from an inexpensive material such as aluminum foil. Films <b>552</b> and <b>554</b> are located on opposite sides of the combination of the phosphor layer <b>560</b><i>b </i>and second electrode <b>542</b>. The second electrode <b>542</b> is also shown with an exposed surface <b>546</b>, accessible through an access opening <b>582</b> in film <b>554</b> for connection to a power source or driver (not shown). Alternatively, the second electrode may be segmented to light up different parts of the device or display independently, in which case, each segment of the second electrode should be electrically connected to the driver.

Segmented Display

First or second electrode <b>540</b>, <b>542</b><i>b </i>enclosed in the housing <b>550</b> can be adapted for a segmented or dot-matrix display. A segmented display may be provided where the electrode is segmented into squares, disks, triangles or other shapes. As shown in <figref idrefs="DRAWINGS">FIG. 18</figref>, a dot matrix display may be provided by segmenting the electrodes <b>540</b>, <b>542</b><i>b </i>into transverse, or as shown here, perpendicular rows and columns. In this arrangement, each segment of the electrodes <b>540</b>, <b>542</b><i>b </i>should have an electrical contact within connector <b>547</b> for connection to a driver <b>544</b>. In a monochrome dot matrix display, the number of horizontal electrodes <b>540</b> is equal to the number of rows of pixels and the number of vertical electrodes <b>542</b><i>b </i>is equal to the number of columns of pixels.

Color Dot Matrix

For color dot-matrix displays, alternating strips or dots of colored phosphor <b>594</b> such as red, green, and blue might be applied to the electroluminescent sheet, as shown on <figref idrefs="DRAWINGS">FIG. 19</figref>. Red, green and blue colored phosphors might be applied, in any order to each pixel. In addition, the first electrode <b>540</b> which is optionally transparent has plural rows of parallel, horizontal electrode strips <b>564</b> connected by a first connector <b>576</b> which may be connected to a first, horizontal controller <b>546</b>. The second, optionally transparent, electrode <b>542</b> has plural columns of parallel, vertical strips <b>542</b><i>a </i>connected by a second connector <b>578</b> to a second, vertical controller <b>548</b> and are transverse or here perpendicular to the rows of electrode <b>540</b>. The numbers of horizontal electrodes <b>540</b> is equal to the number of rows of pixels and the number of vertical electrodes <b>542</b><i>a </i>is three times greater than the number of columns of pixels.

The electroluminescent sheet <b>560</b> with monochrome electroluminescent phosphors might also be used in combination with a non-conductive layer of colored filters <b>594</b> placed outside of and overlying the first electrode <b>540</b> as shown on <figref idrefs="DRAWINGS">FIG. 20</figref> (one color pixel is shown). In this arrangement each of the multi-colored fillers <b>594</b> is associated with a respective first electrode <b>540</b> to provide a color display. Monochrome EL phosphors can be white or of any other color that works efficiently with red, green and blue filters. Unfortunately, some filters can reduce the brightness of an EL device. However, utilization of fluorescent materials or laser dyes that transform light from the electroluminescent sheet <b>560</b> to multiple colors like red, green and blue may also be used to provide a color display, while for higher efficiency and less reduction in brightness. The fluorescent material or laser dyes may be placed outside of the first optionally transparent electrode <b>540</b> instead of using filters <b>594</b> as shown on <figref idrefs="DRAWINGS">FIG. 20</figref>.

While existing EL phosphors have comparably low brightness and lifetime, phosphors for fluorescent and gas discharge devices have high brightness and lifetime. For instance, phosphors for fluorescent devices have brightness characteristics over a thousand Ft-Lamberts and a lifetime of up to 100,000 hours without a change in color. They can be used with devices having suitable EL phosphors which emit light that efficiently activates the fluorescent phosphors. This can be accomplished by replacing the phosphor electroluminescent sheet <b>560</b> with an ultraviolet electroluminescent sheet and using multi-colored fluorescent phosphor (red, green and blue) instead of a colored filter. While fluorescent device phosphors were developed to be activated by ultraviolet light with a 254 nm wavelength peak, their utilization within electroluminescent devices can lead to usage of different wavelengths. The present invention may also be used with real color phosphors or other tri-color systems.

Drivers

Horizontal passive matrix drivers <b>546</b> which control horizontal electrodes, such as the longitudinal electrodes <b>564</b> shown in <figref idrefs="DRAWINGS">FIG. 19</figref>, can be based on shift registers, while vertical drivers <b>548</b> controlling vertical electrodes <b>542</b><i>a </i>may include sample and hold elements equal to the number of pixels in the horizontal row for monochrome displays and three times as much for color displays of the same resolution. In many aspects, these passive matrix drivers <b>546</b>, <b>548</b> are similar to passive matrix LCD drivers, but have a controllable high-voltage output proportional to the brightness of each of the color sub pixels <b>594</b> which combine together as a pixel. As an option, the drivers <b>546</b>, <b>548</b> may have a low-voltage control circuit with high-voltage output transistors or transistor arrays allowing voltages over a kilovolt to be achieved. The electroluminescent apparatus may also use custom designed drivers or existing drivers with some modifications.

CRT Driver

When very high voltages are required, a special cathode ray tube (CRT) driver with electron gun <b>544</b><i>b </i>can be used as shown in the alternative embodiment of <figref idrefs="DRAWINGS">FIG. 21</figref>. In this embodiment, the driver is a cathode ray tube with the electron gun <b>544</b><i>b</i>, a front panel <b>592</b> which is at least partially made of non-conductive material and a plurality of electrodes <b>595</b> which are impregnated within the front panel <b>592</b>, and are connected to electrodes <b>540</b>, or <b>542</b>. As the electron beam <b>590</b> scans the electrodes <b>595</b>, the corresponding pixels of the electroluminescent sheet <b>560</b> (not shown) are activated. The CRT tube driver can be of any conventional design except that wires are impregnated in the front panel <b>592</b> instead of phosphors covering the inside surface. In this configuration, voltages ranging from a few kilovolts to a few dozen kilovolts can be achieved to illuminate the electroluminescent sheet <b>560</b>.

Tiled Electroluminescent Sheet

An increase in the size of an EL sheet <b>630</b> can lead to difficulties and expenses associated with the increased size of the electroluminescent sheet <b>630</b>. In some cases, thin-film phosphors may need to be grown as layered crystals on a second rigid surface, usually glass which may increase the cost of the apparatus. However, an array of comparatively small tiles <b>672</b> may be used for a larger apparatus as illustrated in <figref idrefs="DRAWINGS">FIG. 22</figref>. Each tile <b>672</b> illustrated in <figref idrefs="DRAWINGS">FIGS. 22</figref>, <b>23</b> has a conventional layer of thin-film EL material which is deposited on a rigid substrate such as glass, ceramic plate, plastic, or other insulating material associated with a sheet <b>664</b> of insulating material. Each rear electrode <b>642</b>, for each segment, as shown in <figref idrefs="DRAWINGS">FIG. 23</figref> is connected to corresponding electrical contact (not shown) via conducting component <b>670</b>.

An optionally transparent, first electrode <b>640</b> may be common to plural pixels on the tile <b>672</b>. The EL phosphors for each sub pixel can have different colors or alternating color areas, such as red, green and blue. The first electrodes <b>640</b> of each tile <b>672</b> can be connected together by wires, conductive adhesives or any other means. The electrodes <b>640</b> may also be pressed against another common transparent electrode <b>666</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 25</figref>. All tiles <b>672</b> assembled in one large electroluminescent sheet should be placed in a sealed enclosure to prevent them from damage.

The thin-film EL sheet described above and shown in <figref idrefs="DRAWINGS">FIGS. 22</figref>, <b>23</b> and <b>25</b> is an arrangement for an active matrix display. For the passive matrix activation of the individual pixels, the first electrodes of each tile and the first, common electrode for all tiles should be divided in vertical or horizontal strips of a width equal to the size of each individual sub pixel, providing a sufficient gap between each sub pixels and between each transparent electrode. The invention can also be used with interlaced scanning, dual scanning or other scanning methodologies.

<figref idrefs="DRAWINGS">FIG. 24</figref> illustrates another embodiment of the invention with pixelated second electrode <b>681</b>. A resealable housing has front and rear panels <b>652</b>, <b>654</b> receiving an electroluminescent device <b>662</b> which is presented by the first and second electrodes <b>682</b> and <b>681</b> and electroluminescent sheet <b>660</b>. The electrodes sandwich electroluminescent sheet <b>660</b> therebetween. The first electrode <b>682</b> is illustrated with a continuous electrical contact while the second electrode <b>681</b> has a non-continuous or pixelated surface <b>646</b> which is accessible through the holes <b>678</b> in special non-conductive separating sheet <b>654</b>. Optionally flexible electrode <b>681</b> may be fabricated from double-sized printed circuit board material. Each pixel of electrode <b>681</b> has corresponding contact members or contacts <b>670</b> which maybe connected to a controller or power supply. Contacts <b>670</b> can be electrically connected to pixeled surfaces <b>646</b> if a hole <b>678</b> exists in sheet <b>654</b> (<figref idrefs="DRAWINGS">FIG. 24</figref>). In case of electrical contact, corresponding surface <b>646</b> is connected to a power supply or controller, and this pixel is activated. Optionally, all contacts <b>670</b> can be connected together as shown in dashed lines in <figref idrefs="DRAWINGS">FIG. 24</figref>.

Automatic Brightness Control

As illustrated in the graph of <figref idrefs="DRAWINGS">FIG. 26</figref>, the brightness of electroluminescent phosphors is inversely proportional to its time in operation; the brightness may exponentially decline with time of operation at a constant initial voltage and frequency. However, a constant brightness can be obtained by initially maintaining the brightness of the phosphor at 50-75% of the maximum brightness using a minimum voltage and frequency. Reduction in brightness can be adjusted by increasing the voltage at a constant frequency. After the voltage is increased to its available maximum, frequency may be increased to a reasonable level. This technique requires a very simple circuit of about a dozen transistors with other necessary components that can be fabricated as a comparatively simple and inexpensive multi-channel integrated circuit.

A controller with brightness adjustment electronic circuitry may be coupled to the electroluminescent apparatus such as the one depicted in <figref idrefs="DRAWINGS">FIG. 19</figref>, or any other type mentioned herein or elsewhere. Optionally, a photodiode or phototransistor may provide a feedback or input signal for the automatic brightness adjustment or as a measurement of the impedance of the phosphor.

As illustrated in <figref idrefs="DRAWINGS">FIG. 30</figref>, one or more a photodiodes <b>656</b> may be placed in the housing <b>650</b> against special small control areas <b>657</b> of EL phosphors on the electroluminescent sheet <b>660</b> outside of the work area. The photodiode is generally connected to the driver or controller. For color sheets, there should be control areas for each color. Impedance of the phosphor of the sub pixel can be used because the phosphor's efficiency does not change significantly. As a result, its impedance increases with time of use. This phenomenon can be used for an automatic brightness adjustment. For example, during the duration of one frame, the maximum voltage is applied to all vertical buses. The current through each bus is inversely proportional to the impedance of this sub pixel. This information is stored in a memory and can be used for the automatic brightness adjustment. The described process is only one of many available brightness adjustment systems. The type of system used will depend on the desired level of precision.

Air Evacuation

One or both electrodes or the electroluminescent sheet <b>760</b> can have multiple grooves, channels or holes of any shape and pattern configuration for better evacuation of the air from the envelope as shown in <figref idrefs="DRAWINGS">FIG. 27</figref>. Location of sets of grooves <b>700</b>, <b>702</b> is preferably between segments of each of electrodes <b>704</b>, first or second or both. Surfaces of the envelope can have similar grooves, channels or holes on their inner side. It is noted that, whereas the prior art provided an electroluminescent sheet wherein the phosphor layer is joined to both electrodes which are comparatively expensive compared to the phosphor layer, under the present invention, the sheet comprises a phosphor layer such as sheet <b>60</b> that is not joined to any electrode and can be removed from the housing and replaced without removing the electrodes or alternatively the phosphor layer of sheet <b>560</b> includes a single comparatively non expensive foil joined thereto that can be inexpensively replaced with the phosphor portion of the sheet <b>560</b>. Consequently, in accordance with the invention, the term sheet as used herein preferably means a phosphor layer with no attached electrode or such a sheet with a single attached and disposable electrode.

Grooves on the viewing side can be used for improvement of the viewing angle and uniformity of emitted light. For this purpose, grooves should have a special shape.

It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except insofar as such limitations are included in the following claims and allowable equivalents thereof.